SUMMARY Chemistry and Biology of Mitragynine Alkaloids ! Mitragynine is a corynanthe-type indole alkaloid representing the major psychoactive constituent of Mitragyna speciosa (also known as ?kratom?), a plant native to Southeast Asia. The use of kratom has been on the rise in the U.S. in the last decade, to such an extent that it attracted the attention of the Drug Enforcement Administration (DEA). Despite the initial intent by the DEA to place two alkaloids of this plant, mitragynine and 7-hydroxymitragynine (7OH), into Schedule I of the Control Substance Act, the DEA eventually withdrew this action following dramatic opposition from the public. Thus, kratom remains a readily available ?opioid material? in the U.S. and most other countries worldwide. At the same time, the basic science underlying the biological effects of kratom remains poorly understood. The proposed research addresses an urgent need for a systematic examination of mitragynine alkaloids and builds on extensive preliminary results generated by the PIs. We have recently reported that mitragynine is a partial mu-opioid receptor (MOR) agonist with a G protein-biased signaling profile. In addition, we have found that mitragynine is metabolized to 7OH, a more potent, G protein-biased MOR agonist. Furthermore, we have shown that 7OH induces potent analgesia in mice without respiratory depression and constipation side effects, and thus, represents an attractive atypical opioid template for further investigations. In this application, we focus on mapping the basic science of mitragynine and its metabolite 7OH in terms of synthetic methods, metabolism, receptor signaling and pharmacological profile,!by pursuing three integrated aims. Moreover, we aim to explore the central hypothesis that G protein-biased MOR agonism underlies the favorable separation of analgesia and side effects exhibited by mitragynine-type compounds. These goals will be accomplished by an interdisciplinary team with significant experience in synthetic and computational chemistry, opioid receptor signaling, and in vitro and in vivo pharmacology.